It's an 80's cartoon, so nothing in depth for the show was ever established, except that she threw the king into an alternate dimension and imprisoned him there to weaken the Palace of Power. The closest we get is from the game itself:
Which says that she possibly came from a human brain that went insane. As the show is based on the games, it could be reasonable to assume it would transfer. The show did take some pretty weird liberties with the characters, though (see Simon Belmont, holy shit).
I don't think this relates to fanon/headcanon to assume that she had some sort of vague origin as opposed to just popping into existence with all her resources and influence. As she'd be permanently losing the memories due to the new rules saying the price can't be regained without a charm wish (something that would never happen), any background details she has wouldn't be played out or even mentioned, so it's not a violation of the rules.
no subject
https://en.wikipedia.org/wiki/Mother_Brain#Concept_and_characteristics
Which says that she possibly came from a human brain that went insane. As the show is based on the games, it could be reasonable to assume it would transfer. The show did take some pretty weird liberties with the characters, though (see Simon Belmont, holy shit).
I don't think this relates to fanon/headcanon to assume that she had some sort of vague origin as opposed to just popping into existence with all her resources and influence. As she'd be permanently losing the memories due to the new rules saying the price can't be regained without a charm wish (something that would never happen), any background details she has wouldn't be played out or even mentioned, so it's not a violation of the rules.